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Aviation History
1949
1949 - 1131.PDF
7i6 FLIGHT JUNE IOTH, 1949 Joint Conference and proved to have lost very little in power compared with the power developed as a new engine, the fuel and oil con- sumptions showing no appreciable change (Fig. 3). Dealing with icing experience on the Theseus, the lecturer stated that, on one flight, the port Theseus engine cut out at 20,500ft due to a.n interruption in the fuel supply. This altitude had been reached on account of weather, but with only three engines functioning it was impossible to maintain height and a forced descent through cloud was made from 20,500ft down to 12,000ft. At 19,000ft and an ambient air temperature of -7 deg C, rime ice began to form on the leading-edges of the wings, on the airscrew spinners and on the leading-edges of all engine cowlings. The starboard Theseus engine could be seen from the cockpit, and it was noted that during the descent the ice began to form on the stoneguard, starting on the outer circumference. The build-up of ice, however, ceased at about once inch from the spinner fairing, leaving an annulus of this width free of ice, despite the fact that the remainder of the guard had a deposited ice layer of at least one inch thickness. This annulus was obviously kept clear of ice because of the spinner boundary layer, with a contribution from centrifugal effects, and it was fortunate that it enabled the engine to continue running. In fact, the engine r.p.m. of 7,000 was not only maintained constant throughout the descent, but no indication of altered performance due to icing was observed on the instru- mentation provided in the aircraft. Uncritical Icing The important factor to note was not that an ice-free annulus was maintained around the spinner, although it might be possible to make use of this feature for warm-air dilution, but that ice did not pass into the engine in solid pieces either during the forming or the dispersal process, and that there was no sign whatever of ice damage to the compressor blading on subsequent inspection. This was the second occasion on which ice had formed on the guard at the entry to the air intake, the first being on the test bed, and on this occasion there had been no sign whatever of damage to the compressor blading. Turning to the condition of the engines after flight, Mr. Owner recalled that, at the conclusion of the special 500-hour test, the condition of the Theseus test-bed engine was similar to that of the two flight-engines described, with particular reference to the reduction gear, combustion chambers and turbine assembly. It was considered that, after a certain period of running, during which the engine settled down, subsequent deterioration was very slow, and it was hoped to prove this point during the next few months with Transport Command. A certain amount of tropical operational experience with the Theseus-Lincoln was obtained, said the lecturer, since the Transport Command route for the aircraft stretched as far as Fayid in the Suez Canal Zone, and an assessment was made of performance deterioration with temperature rise. Due to the rather unreliable nature of the instruments, it was thought advisable not to rely upon a single set of observa- tions, but to take the tropical observations in bulk, and derive the horse-power and specific consumption curves at various temperatures and different heights. From these it transpired that approximately 1 per cent of power was lost for each degree of temperature rise. This was rather less than the static power loss with rises in temperature, which approxi- mated to ij per cent for each degree. It had to be pointed out that the 1 per cent power loss per deg C appertained to a forward speed of 270 m.p.h. «, Mr. Owner then gave some general conclusions to be drawn from the fact that more than 1,000 hour-6' operational engine flying had been successfully completed during a period of eight months by an entirely new form of power unit in the hands of R.A.F. personnel operating under Service conditions. In this time, the performance of the Theseus had been exceed- ingly satisfactory, and it had given virtually no trouble whatso- ever. The very small maintenance claimed for this type of engine had been well substantiated during the course of the trials, and the conditions of engines after more than 200 hours' flying led to the firm belief that overhaul costs, in spite of long life between them, would be economical compared with those foi piston engines. Improvement in operating characteristics, such as reduced fuel consumption, ease and simplicity of control and satisfac- tory functioning in climatic conditions should be achieved within a relatively short period. The trifling oil consumption throughout 200 hours' flying, and the fact that the consump- tion was less at the end of this period than when the engine was new, was an economy in operation never experienced in piston engines of equivalent power. Since a power plant was not designed especially for the present installation and the type of power plant already in use in the Theseus-Lincoln was fitted, the maintenance time for removal of cowlings and other inspection requirements was greater than would have been the case on a redesigned unit. Useful experience was gained in this respect, permitting the elimination of such shortcomings in the design of the Theseus units to be fitted to the Handley Page Hermes V. Turning to prospects in the future, the lecturer concluded by stating that the development of the engine itself was proceeding apace, and the addition of protection against icing, reversing airscrews for braking, gear boxes, and cabin blower drives was well under way. When these had achieved a degree of development corresponding to that of the engine, a power plant which was mechanically safe and suitable for both military and civil air transport would have been produced. Fuel consumption was, as ever, the burning question (in more senses than one), and here, in fairness, it had to be reiterated that the tests reported were quite unrepresentative. Whilst it was true that the aircraft concerned had an en- durance well in excess of 10 hours and, apart from the dictates of prudence, could probably have made the England-Egypt run non-stop, they were fitted with long-range tanks to compensate for the fact that the consumption of their early experimental engines was appreciably in excess of that proved to be possible on later marks of engines; a further reduction had already been proved experimentally to be possible within the framework of the existing design. There was, of course, no reason to doubt the theoretical conclusions, which indicated that, with the component effi- ciencies already established, it should be possible to achieve a substantial further reduction in consumption by proper matching and detailed design of the various sections of the engine, without going beyond the stress and temperature limitations covering the body of satisfactory operational ex- perience built up to date. When the potential improvements, such as blade cooling (which yielded far more dividends on the turboprop than on the "pure" jet engine), higher speed, more compact design, etc., were taken into account, it was the author's firm conviction that the turboprop had a very bright future before it, and it was reasonable to hope that it would have a considerable length of useful life before it was finally superseded by the "pure" jet. LANDPLANE v. FLYING BOAT Mr. Keith-Lucas' Paper THE paper read by Mr. D. Keith-Lucas was entitled TheRelative Efficiencies of La?ge Landplanes and Flying Boats. A large part was devoted to the justification of theassumptions made in comparing projected landplants with equivalent flying boats. The lecturer began by making a brief study of the effect olsize on land animals and aquatic animals. He then carried the analogy to surface transport—ships and road vehicles—inorder to show that, instead of following the square-cube law, percentage structure weight tended actually to fall with in-creased size for ships, road vehicles and aquatic animals, but for aircraft and land animals it remained sensibly constant. The most important square-cube law assumption, he said,was that structure was everywhere the ideal structure and working at the maximum allowable stress throughout. Thisassumption was vital if we were to assess at all accurately the effect of loads and dimensions on structure weight; it was,nevertheless, a long way from the truth for anything made by man, and was almost certainly the main reason why thesquare-cube law was not followed in practice. It had also to be assumed that the loads imposed on thestructure were in accordance with the laws of similarity. In fact, they were not, for the range of weights to which wehad built aircraft up to now. Stressing factors had decreased somewhat arbitrarily with increase of size, but this was aprocess which could not continue much farther. Lastly, it had to be assumed that the same materials were used for largeaircraft as for small, but this also was not necessarily true. It was quite common for the larger aircraft to employ highergrade materials, but on examination of the stiffness criteria, 110 help from these high grade materials could be found, becausethe modulus of elasticity had been, up to the present time, as immutable as the laws of the Medes and Persians. The lecturer then made a comparison between design studies
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